In conventional scanning inkjet printers, inkjet printheads typically move across print media depositing ink droplets one swath at a time to form a desired image on a printing medium. A printhead is sometimes in the art also referred to as a pen. In a color printer, several such printheads or pens may be positioned adjacent to one another, each one corresponding to one basic color, and may together travel across the printing medium. In a conventional inkjet printer, each printhead comprises a series of ink-ejecting nozzles and a corresponding plurality of ejection chambers associated with the nozzles. Ink is supplied to the ejection chamber from an ink reservoir, such as an ink cartridge. In thermal inkjet printheads, a firing resistor is located adjacent to the ejection chamber, and may be selectively energized to heat ink in the ejection chamber to a boiling point, which forces an ink droplet to be ejected through the associated nozzle. Piezoelectric printheads use a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the piezoelectric material changes shape, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle.
During the printing, the printhead usually heats up, both due to the operation of the firing resistors (in thermal printers) as well as due to the heat generated by the mechanical movement of the printer and power dissipation from the electronics circuits. When the temperature of the printhead varies, so does the ink viscosity.